<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 200px;
            height: 200px;
            background-color: red;
            margin: 0 auto;
            border-radius: 50%;
            box-shadow: 10px 10px 10px #999;
            animation: my_animation 1s ease-in-out 0.1s infinite alternate paused;
        }
        div:hover{
            animation-play-state: running;
        }
        @keyframes my_animation{
            from{
                opacity: .2;
                box-shadow: 10px 10px 10px rgba(99,99,99,0.1);
            }
            50%{
                opacity: .5;
                box-shadow: 10px 10px 10px rgba(99,99,99,0.76);
            }
            to{
                opacity: 1;
                box-shadow: 10px 10px 10px rgba(99,99,99,1);
                width: 300px;
                height: 300px;
            }
        }
    </style>
</head>
<body>
    <div></div>
</body>
</html>